The long term objective of our laboratory is to determine the mechanism by which the novel c- Myc-interacting tumor suppressor Bin1 renders chemoresistant cancer cells sensitive to DNA- damaging agents such as cisplatin. This project is innovative because it focuses on the 'c-Myc- Bin1-PARP-1'chemoresistant axis, which provides a new and substantially different way of addressing the problem of cisplatin-resistant cancers. We propose to test the hypothesis that the sensitivity of human cancer cells to cisplatin is dependent on the expression of Bin1, a protein that inhibits c-Myc-induced poly(ADP-ribose) polymerase-1 (or PARP-1) activity. Results from our laboratory support our assertion that Bin1 interacts with and inhibits PARP-1, a key nuclear enzyme required for promoting DNA repair. Subsequently, Bin1 decreases chromosome stability and sensitizes cancer cells to cisplatin. Moreover, elevated c-Myc directly represses Bin1 promoter, which subsequently rescues PARP-1 activity and increases cisplatin resistance. We aim to 1) determine the mechanism(s) by which Bin1 suppresses PARP-1-mediated DNA repair, and 2) identify the mechanism(s) by which oncogenic c-Myc alters Bin1 and PARP-1 levels. To achieve the first aim, we will investigate (i) whether the interactions between the automodification domain of PARP-1 and Bin1 are direct and (ii) how Bin1 disrupts the PARP-1-XRCC1 interaction in vivo, an essential step for PARP-1-mediated base excision repair (BER). Given that Bin1 suppresses PARP-1 auto-poly(ADP-ribosyl)ation, we predict that Bin1 inhibits PARP-1-associated XRCC1 recruitment and the subsequent BER pathways. To identify the mechanism by which elevated c- Myc alters Bin1 and PARP-1 expression, we will determine how c-Myc interferes with the transcriptional activities of Miz-1 and E2F1, two transcription factors that separately activate the Bin1 promoter, and conversely, how c-Myc upregulates PARP-1 expression via Brahma-related gene protein 1 (BRG1), a key component of the SWI/SNF chromatin remodeling complex. Cisplatin-induced cell death assays in the presence and absence of small interfering RNAs or chemical inhibitors of Bin1, PARP-1, and c-Myc will determine the manner by which Bin1 disrupts the 'c-Myc-PARP-1'chemoresistant axis. Successful completion of this project will define Bin1-mediated chemosensitizing mechanisms that attenuate PARP-1-mediated DNA repair. This knowledge will be significant, as it may guide the development of therapeutic strategies for the treatment of cisplatin-resistant human cancers that overexpress c-Myc. PUBLIC HEALTH RELEVANCE: Cisplatin, an anti-neoplastic DNA-damaging agent, is one of the main lines of treatment used in cancer chemotherapy. However, many cancers acquire cisplatin resistance, which eventually causes treatment failure. Our study will determine how cancer becomes resistant to cisplatin, and how we can re-sensitize chemoresistant cancer to cisplatin.